t-drivers: deactivate loopback testing for older kernels

ETH_TEST_FL_EXTERNAL_LB and ETH_TEST_FL_EXTERNAL_LB_DONE are not
available in kernel version < 3.1.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat-drivers: refresh alx patches

This was done against alx-20130124.